Regulation of flotillin-1 in the establishment of NIH-3T3 cell-cell interactions.

Flotillin-1 is a lipid raft-associated protein involved in neuronal regeneration, insulin signaling in adipocytes, and phagosome maturation in macrophages. We detected abundant flotillin-1 mRNA expression in confluent cultures of mouse NIH-3T3 fibroblasts. These cells were used as a model to assess the regulation of flotillin-1 mRNA and protein expression by cell-cell interactions. The disruption of cell-cell interactions triggered the downregulation of the flotillin-1 gene. However, the establishment of new cell interactions, and finally confluence, increased both the flotillin-1 transcript and its protein. Despite flotillin-1 having been described as an integral protein of the cell membrane, it is also very conspicuous in the hydrophilic fraction (the non-membrane fraction) of confluent cell extracts. The promoter region of the flotillin-1 gene was isolated and analyzed by transfection experiments, and the regulatory domains containing motifs for binding transcription factors involved in cell differentiation were identified.